CAUSES OF DEGENERATION IN BLIND FISHES. 397 



CAUSES OF DEGENERATION IN BLIND FISHES. 



By Professor CARL H. EIGENMANN, 



INDIANA UNIVERSITY. 



IT may now be profitable to take up the causes leading to the small 

 degree of degeneration found in Chologaster, the degenerations of 

 the eye in Amblyopsis, Typhlichthys and Troglichthys to a mere 

 vestige, together with the total disappearance of some of the accessory 

 structures of the eye, as the muscles. 



In the outset of this consideration we must guard against the almost 

 universal supposition that animals depending on their eyes for food are 

 or have been colonizing caves, or that the blind forms are the results 

 of catastrophes that have happened to eyed forms depending on their 

 eyesight for their existence. This idea, so prevalent, vitiates nearly 

 everything that has been written on the degeneration of the eyes of 

 cave animals. 



Another word of warning ought perhaps to be added. The process 

 of degeneration found in the Amblyopsidae need not necessarily be ex- 

 pected to be identical with the degeneration of the same organs in an- 

 other group of animals, and, however much the conditions in one group 

 may illuminate the conditions in another, cross-country conclusions 

 must be guarded against. 



The degeneration of organs ontogenetically and phylogenetically 

 has received a variety of explanations: 



1. The organ diminishes with disuse (ontogenetic degeneration) — 

 Lamarck, Eoux, Packard), and the effect of this disuse appears to some 

 extent in the next generation (phylogenetic degeneration — Lamarck, 

 Roux, Packard, Kohl). 



2. Through a condition of panmixia the general average maintained 

 by selection is reduced to the birth mean in one generation (ontogenetic 

 — Romanes, Lankester, Lloyd Morgan, Weismann) to the greatest pos- 

 sible degeneration in succeeding generations (phylogenetic — Weis- 

 mann), or but little below the birth average of the first generation 

 (Weismann's later view, Romanes, Morgan, Lankester). 



3. Through natural selection (reversed), the struggle of persons, the 

 organ may be caused to degenerate either (A) by the migration of 

 persons with highly developed eyes from the colony living in the dark 

 (Lankester), or (B) through economy of weight and nutriment or lia- 

 bility to injury (phylogenetic purely — Darwin, Romanes). 



4. Through the struggle of parts for room or for food an unused 



